743 lines
28 KiB
Text
743 lines
28 KiB
Text
<!-- $FreeBSD: doc/en_US.ISO_8859-1/articles/multi-os/article.sgml,v 1.13 2000/07/26 18:24:49 jim Exp $ -->
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<!DOCTYPE ARTICLE PUBLIC "-//FreeBSD//DTD DocBook V4.1-Based Extension//EN">
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<article>
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<articleinfo>
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<title>Installing and Using FreeBSD With Other Operating Systems</title>
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<authorgroup>
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<author>
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<firstname>Jay</firstname>
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<surname>Richmond</surname>
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<affiliation>
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<address>
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<email>jayrich@sysc.com</email>
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</address>
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</affiliation>
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</author>
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</authorgroup>
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<pubdate>6 August 1996</pubdate>
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<abstract>
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<para>This document discusses how to make FreeBSD coexist nicely
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with other popular operating systems such as Linux, MS-DOS,
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OS/2, and Windows 95. Special thanks to: Annelise Anderson
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<email>andrsn@stanford.edu</email>, Randall Hopper
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<email>rhh@ct.picker.com</email>, and Jordan K. Hubbard
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<email>jkh@time.cdrom.com</email></para>
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</abstract>
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</articleinfo>
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<sect1>
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<title>Overview</title>
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<para>Most people can't fit these operating systems together
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comfortably without having a larger hard disk, so special
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information on large EIDE drives is included. Because there are
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so many combinations of possible operating systems and hard disk
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configurations, the <xref linkend="ch5"> section may be of the
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most use to you. It contains descriptions of specific working
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computer setups that use multiple operating systems.</para>
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<para>This document assumes that you have already made room on
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your hard disk for an additional operating system. Any time you
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repartition your hard drive, you run the risk of destroying the
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data on the original partitions. However, if your hard drive is
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completely occupied by DOS, you might find the FIPS utility
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(included on the FreeBSD CD-ROM in the
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<filename>\TOOLS</filename> directory or via <ulink
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URL="ftp://ftp.FreeBSD.org/pub/FreeBSD/tools">ftp</ulink>)
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useful. It lets you repartition your hard disk without
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destroying the data already on it. There is also a commercial
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program available called Partition Magic, which lets you size
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and delete partitions without consequence.</para>
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</sect1>
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<sect1 id="ch2">
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<title>Overview of Boot Managers</title>
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<para>These are just brief descriptions of some of the different
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boot managers you may encounter. Depending on your computer
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setup, you may find it useful to use more than one of them on
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the same system.</para>
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<variablelist>
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<varlistentry>
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<term>Boot Easy</term>
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<listitem>
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<para>This is the default boot manager used with FreeBSD.
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It has the ability to boot most anything, including BSD,
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OS/2 (HPFS), Windows 95 (FAT and FAT32), and Linux.
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Partitions are selected with the function keys.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>OS/2 Boot Manager</term>
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<listitem>
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<para>This will boot FAT, HPFS, FFS (FreeBSD), and EXT2
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(Linux). It will also boot FAT32 partitions. Partitions
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are selected using arrow keys. The OS/2 Boot Manager is
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the only one to use its own separate partition, unlike the
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others which use the master boot record (MBR). Therefore,
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it must be installed below the 1024th cylinder to avoid
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booting problems. It can boot Linux using LILO when it is
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part of the boot sector, not the MBR. Go to <ulink
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URL="http://www.linuxresources.com/LDP/HOWTO/HOWTO-INDEX.html">Linux
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HOWTOs</ulink> on the World Wide Web for more
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information on booting Linux with OS/2's boot
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manager.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>OS-BS</term>
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<listitem>
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<para>This is an alternative to Boot Easy. It gives you more
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control over the booting process, with the ability to set
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the default partition to boot and the booting timeout.
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The beta version of this programs allows you to boot by
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selecting the OS with your arrow keys. It is included on
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the FreeBSD CD in the <filename>\TOOLS</filename>
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directory, and via <ulink
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URL="ftp://ftp.FreeBSD.org/pub/FreeBSD/tools">ftp</ulink>.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>LILO, or LInux LOader</term>
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<listitem>
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<para>This is a limited boot manager. It will boot FreeBSD,
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though some customization work is required in the LILO
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configuration file.</para>
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</listitem>
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</varlistentry>
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</variablelist>
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<note id="fat32">
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<title>About FAT32</title>
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<para>FAT32 is the replacement to the FAT filesystem included in
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Microsoft's OEM SR2 Beta release, which is expected to be
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utilitized on computers pre-loaded with Windows 95 towards the
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end of 1996. It converts the normal FAT file system and
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allows you to use smaller cluster sizes for larger hard
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drives. FAT32 also modifies the traditional FAT boot sector
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and allocation table, making it incompatible with some boot
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managers.</para>
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</note>
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</sect1>
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<sect1 id="ch3">
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<title>A Typical Installation</title>
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<para>Let's say I have two large EIDE hard drives, and I want to
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install FreeBSD, Linux, and Windows 95 on them.</para>
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<para>Here's how I might do it using these hard disks:</para>
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<itemizedlist>
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<listitem>
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<para><filename>/dev/wd0</filename> (first physical hard disk)</para>
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</listitem>
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<listitem>
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<para><filename>/dev/wd1</filename> (second hard disk)</para>
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</listitem>
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</itemizedlist>
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<para>Both disks have 1416 cylinders.</para>
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<procedure>
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<step>
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<para>I boot from a MS-DOS or Windows 95 boot disk that
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contains the <filename>FDISK.EXE</filename> utility and make a small
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50 meg primary partition (35-40 for Windows 95, plus a
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little breathing room) on the first disk. Also create a
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larger partition on the second hard disk for my Windows
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applications and data.</para>
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</step>
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<step>
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<para>I reboot and install Windows 95 (easier said than done)
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on the <filename>C:</filename> partition.</para>
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</step>
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<step>
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<para>The next thing I do is install Linux. I'm not sure
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about all the distributions of Linux, but slackware includes
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LILO (see <xref linkend="ch2">). When I am partitioning out
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my hard disk with Linux <command>fdisk</command>, I would
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put all of Linux on the first drive (maybe 300 megs for a
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nice root partition and some swap space).</para>
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</step>
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<step>
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<para>After I install Linux, and are prompted about installing
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LILO, make SURE that I install it on the boot sector of my
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root Linux partition, not in the MBR (master boot
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record).</para>
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</step>
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<step>
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<para>The remaining hard disk space can go to FreeBSD. I also
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make sure that my FreeBSD root slice does not go beyond the
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1024th cylinder. (The 1024th cylinder is 528 megs into the
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disk with our hypothetical 720MB disks). I will use the
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rest of the hard drive (about 270 megs) for the
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<filename>/usr</filename> and <filename>/</filename> slices if I wish. The
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rest of the second hard disk (size depends on the amount of
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my Windows application/data partition that I created in step
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1 can go to the <filename>/usr/src</filename> slice and swap
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space.</para>
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</step>
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<step>
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<para>When viewed with the Windows 95 <command>fdisk</command>
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utility, my hard drives should now look something like this:
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<screen>
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---------------------------------------------------------------------
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Display Partition Information
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Current fixed disk drive: 1
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Partition Status Type Volume_Label Mbytes System Usage
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C: 1 A PRI DOS 50 FAT** 7%
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2 A Non-DOS (Linux) 300 43%
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Total disk space is 696 Mbytes (1 Mbyte = 1048576 bytes)
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Press Esc to continue
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---------------------------------------------------------------------
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Display Partition Information
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Current fixed disk drive: 2
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Partition Status Type Volume_Label Mbytes System Usage
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D: 1 A PRI DOS 420 FAT** 60%
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Total disk space is 696 Mbytes (1 Mbyte = 1048576 bytes)
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Press Esc to continue
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---------------------------------------------------------------------
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</screen>
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** May say FAT16 or FAT32 if you are using the OEM SR2
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update. See <xref linkend="ch2">).</para>
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</step>
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<step>
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<para>Install FreeBSD. I make sure to boot with my first hard
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disk set at <quote>NORMAL</quote> in the BIOS. If it is not,
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I'll have the enter my true disk geometry at boot time (to
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get this, boot Windows 95 and consult Microsoft Diagnostics
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(<filename>MSD.EXE</filename>), or check your BIOS) with the
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parameter <literal>hd0=1416,16,63</literal> where
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<replaceable>1416</replaceable> is the number of cylinders on my hard
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disk, <replaceable>16</replaceable> is the number of heads per track,
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and <replaceable>63</replaceable> is the number of sectors per track on
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the drive.</para>
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</step>
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<step>
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<para>When partitioning out the hard disk, I make sure to
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install Boot Easy on the first disk. I don't worry about
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the second disk, nothing is booting off of it.</para>
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</step>
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<step>
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<para>When I reboot, Boot Easy should recognize my three
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bootable partitions as DOS (Windows 95), Linux, and BSD
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(FreeBSD).</para>
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</step>
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</procedure>
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</sect1>
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<sect1 id="ch4">
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<title>Special Considerations</title>
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<para>Most operating systems are very picky about where and how
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they are placed on the hard disk. Windows 95 and DOS need to be
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on the first primary partitiin on the first hard disk. OS/2 is
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the exception. It can be installed on the first or second disk
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in a primary or extended partition. If you are not sure, keep
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the beginning of the bootable partitions below the 1024th
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cylinder.</para>
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<para>If you install Windows 95 on an existing BSD system, it will
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<quote>destroy</quote> the MBR, and you will have to reinstall your
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previous boot manager. Boot Easy can be reinstalled by using
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the BOOTINST.EXE utility included in the \TOOLS directory on the
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CD-ROM, and via <ulink
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URL="ftp://ftp.FreeBSD.org/pub/FreeBSD/tools">ftp</ulink>.
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You can also re-start the installation process and go to the
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partition editor. From there, mark the FreeBSD partition as
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bootable, select Boot Manager, and then type W to (W)rite out
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the information to the MBR. You can now reboot, and Boot Easy
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should then recognize Windows 95 as DOS.</para>
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<para>Please keep in mind that OS/2 can read FAT and HPFS
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partitions, but not FFS (FreeBSD) or EXT2 (Linux) partitions.
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Likewise, Windows 95 can only read and write to FAT and FAT32
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(see <xref linkend="ch2">) partitions. FreeBSD can read most
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file systems, but currently cannot read HPFS partitions. Linux
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can read HPFS partitions, but can't write to them. Recent
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versions of the Linux kernel (2.x) can read and write to Windows
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95 VFAT partitions (VFAT is what gives Windows 95 long file
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names - it's pretty much the same as FAT). Linux can read and
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write to most file systems. Got that? I hope so.</para>
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</sect1>
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<sect1 id="ch5">
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<title>Examples</title>
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<para><emphasis>(section needs work, please send your example to
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<email>jayrich@sysc.com</email>)</emphasis>.</para>
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<para>FreeBSD+Win95: If you installed FreeBSD after Windows 95,
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you should see <literal>DOS</literal> on the Boot Easy menu. This is
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Windows 95. If you installed Windows 95 after FreeBSD, read
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<xref linkend="ch4"> above. As long as your hard disk does not
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have 1024 cylinders you should not have a problem booting. If
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one of your partitions goes beyond the 1024th cylinder however,
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and you get messages like <errorname>invalid system disk</errorname>
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under DOS (Windows 95) and FreeBSD will not boot, try looking
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for a setting in your BIOS called <quote>> 1024 cylinder
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support</quote> or <quote>NORMAL/LBA</quote> mode. DOS may need LBA
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(Logical Block Addressing) in order to boot correctly. If the
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idea of switching BIOS settings every time you boot up doesn't
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appeal to you, you can boot FreeBSD through DOS via the
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<filename>FBSDBOOT.EXE</filename> utility on the CD (It should find your
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FreeBSD partition and boot it.)</para>
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<para>FreeBSD+OS/2+Win95: Nothing new here. OS/2's boot manger
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can boot all of these operating systems, so that shouldn't be a
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problem.</para>
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<para>FreeBSD+Linux: You can also use Boot Easy to boot both
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operating systems.</para>
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<para>FreeBSD+Linux+Win95: (see <xref linkend="ch3">)</para>
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</sect1>
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<sect1 id="sources">
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<title>Other Sources of Help</title>
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<para>There are many <ulink
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URL="http://www.linuxresources.com/LDP/HOWTO/HOWTO-INDEX.html">Linux
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HOW-TOs</ulink> that deal with multiple operating systems on
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the same hard disk.</para>
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<para>The <ulink
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URL="http://www.linuxresources.com/LDP/HOWTO/mini/Linux+DOS+Win95+OS2.html">Linux+DOS+Win95+OS2
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mini-HOWTO</ulink> offers help on configuring the OS/2 boot
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manager, and the <ulink
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URL="http://www.linuxresources.com/LDP/HOWTO/mini/Linux+FreeBSD.html">Linux+FreeBSD
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mini-HOWTO</ulink> might be interesting as well. The <ulink
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URL="http://www.in.net/~jkatz/win95/Linux-HOWTO.html">Linux-HOWTO</ulink>
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is also helpful.</para>
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<para>The <ulink
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URL="http://www.dorsai.org/~dcl/publications/NTLDR_Hacking">NT
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Loader Hacking Guide</ulink> provides good information on
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multibooting Windows NT, '95, and DOS with other operating
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systems.</para>
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<para>And Hale Landis's "How It Works" document pack contains some
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good info on all sorts of disk geometry and booting related
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topics. You can find it at
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<ulink
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URL="ftp://fission.dt.wdc.com/pub/otherdocs/pc_systems/how_it_works/allhiw.zip">ftp://fission.dt.wdc.com/pub/otherdocs/pc_systems/how_it_works/allhiw.zip</ulink>.</para>
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<para>Finally, don't overlook FreeBSD's kernel documentation on
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the booting procedure, available in the kernel source
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distribution (it unpacks to <ulink
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URL="file:/usr/src/sys/i386/boot/biosboot/README.386BSD">file:/usr/src/sys/i386/boot/biosboot/README.386BSD</ulink>.</para>
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</sect1>
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<sect1>
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<title>Technical Details</title>
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<para><emphasis>(Contributed by Randall Hopper,
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<email>rhh@ct.picker.com</email>)</emphasis></para>
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<para>This section attempts to give you enough basic information
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about your hard disks and the disk booting process so that you
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can troubleshoot most problems you might encounter when getting
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set up to boot several operating systems. It starts in pretty
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basic terms, so you may want to skim down in this section until
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it begins to look unfamiliar and then start reading.</para>
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<sect2>
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<title>Disk Primer</title>
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<para>Three fundamental terms are used to describe the location
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of data on your hard disk: Cylinders, Heads, and Sectors.
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It's not particularly important to know what these terms
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relate to except to know that, together, they identify where
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data is physically on your disk.</para>
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<para>Your disk has a particular number of cylinders, number of
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heads, and number of sectors per cylinder-head (a
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cylinder-head also known nown as a track). Collectively this
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information defines the "physical disk geometry" for your hard
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disk. There are typically 512 bytes per sector, and 63
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sectors per track, with the number of cylinders and heads
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varying widely from disk to disk. Thus you can figure the
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number of bytes of data that'll fit on your own disk by
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calculating:</para>
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<informalexample>
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<para>(# of cylinders) × (# heads) × (63
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sectors/track) × (512 bytes/sect)</para>
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</informalexample>
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<para>For example, on my 1.6 Gig Western Digital AC31600 EIDE hard
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disk,that's:</para>
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<informalexample>
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<para>(3148 cyl) × (16 heads) × (63
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sectors/track) × (512 bytes/sect)</para>
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</informalexample>
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<para>which is 1,624,670,208 bytes, or around 1.6 Gig.</para>
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<para>You can find out the physical disk geometry (number of
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cylinders, heads, and sectors/track counts) for your hard
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disks using ATAID or other programs off the net. Your hard
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disk probably came with this information as well. Be careful
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though: if you're using BIOS LBA (see <xref
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linkend="limits">), you can't use just any program to get
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the physical geometry. This is because many programs (e.g.
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<filename>MSD.EXE</filename> or FreeBSD fdisk) don't identify the
|
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physical disk geometry; they instead report the
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<firstterm>translated geometry</firstterm> (virtual numbers from using
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LBA). Stay tuned for what that means.</para>
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<para>One other useful thing about these terms. Given 3
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numbers—a cylinder number, a head number, and a
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sector-within-track number—you identify a specific
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absolute sector (a 512 byte block of data) on your disk.
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Cylinders and Heads are numbered up from 0, and Sectors are
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numbered up from 1.</para>
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<para>For those that are interested in more technical details,
|
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information on disk geometry, boot sectors, BIOSes, etc. can
|
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be found all over the net. Query Lycos, Yahoo, etc. for
|
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<literal>boot sector</literal> or <literal>master boot record</literal>.
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Among the useful info you'll find are Hale Landis's
|
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<citetitle>How It Works</citetitle> document pack. See the <xref
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linkend="sources"> section for a few pointers to this
|
|
pack.</para>
|
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|
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<para>Ok, enough terminology. We're talking about booting
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here.</para>
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</sect2>
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<sect2 id="booting">
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<title>The Booting Process</title>
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<para>On the first sector of your disk (Cyl 0, Head 0, Sector 1)
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lives the Master Boot Record (MBR). It contains a map of your
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disk. It identifies up to 4 <firstterm>partitions</firstterm>, each of
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which is a contiguous chunk of that disk. FreeBSD calls
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partitions <firstterm>slices</firstterm> to avoid confusion with it's
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own partitions, but we won't do that here. Each partition can
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contain its own operating system.</para>
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<para>Each partition entry in the MBR has a <firstterm>Partition
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ID</firstterm>, a <firstterm>Start Cylinder/Head/Sector</firstterm>, and an
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<firstterm>End Cylinder/Head/Sector</firstterm>. The Partition ID
|
|
tells what type of partition it is (what OS) and the Start/End
|
|
tells where it is. <xref linkend="tbl-pid"> lists a
|
|
smattering of some common Partition IDs.</para>
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<table id="tbl-pid">
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<title>Partition IDs</title>
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<tgroup cols="2">
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<thead>
|
|
<row>
|
|
<entry>ID (hex)</entry>
|
|
<entry>Description</entry>
|
|
</row>
|
|
</thead>
|
|
|
|
<tbody>
|
|
<row>
|
|
<entry>01</entry>
|
|
<entry>Primary DOS12 (12-bit FAT)</entry>
|
|
</row>
|
|
|
|
<row>
|
|
<entry>04</entry>
|
|
<entry>Primary DOS16 (16-bit FAT)</entry>
|
|
</row>
|
|
|
|
<row>
|
|
<entry>05</entry>
|
|
<entry>Extended DOS</entry>
|
|
</row>
|
|
|
|
<row>
|
|
<entry>06</entry>
|
|
<entry>Primary big DOS (> 32MB)</entry>
|
|
</row>
|
|
|
|
<row>
|
|
<entry>0A</entry>
|
|
<entry>OS/2</entry>
|
|
</row>
|
|
|
|
<row>
|
|
<entry>83</entry>
|
|
<entry>Linux (EXT2FS)</entry>
|
|
</row>
|
|
|
|
<row>
|
|
<entry>A5</entry>
|
|
<entry>FreeBSD, NetBSD, 386BSD (UFS)</entry>
|
|
</row>
|
|
</tbody>
|
|
</tgroup>
|
|
</table>
|
|
|
|
<para>Note that not all partitions are bootable (e.g. Extended
|
|
DOS). Some are—some aren't. What makes a partition
|
|
bootable is the configuration of the <firstterm>Partition Boot
|
|
Sector</firstterm> that exists at the beginning of each
|
|
partition.</para>
|
|
|
|
<para>When you configure your favorite boot manager, it looks up
|
|
the entries in the MBR partition tables of all your hard disks
|
|
and lets you name the entries in that list. Then when you
|
|
boot, the boot manager is invoked by special code in the
|
|
Master Boot Sector of the first probed hard disk on your
|
|
system. It looks at the MBR partition table entry
|
|
corresponding to the partition choice you made, uses the Start
|
|
Cylinder/Head/Sector information for that partition, loads up
|
|
the Partition Boot Sector for that partition, and gives it
|
|
control. That Boot Sector for the partition itself contains
|
|
enough information to start loading the operating system on
|
|
that partition.</para>
|
|
|
|
<para>One thing we just brushed past that's important to know.
|
|
All of your hard disks have MBRs. However, the one that's
|
|
important is the one on the disk that's first probed by the
|
|
BIOS. If you have only IDE hard disks, its the first IDE disk
|
|
(e.g. primary disk on first controller). Similarly for SCSI
|
|
only systems. If you have both IDE and SCSI hard disks
|
|
though, the IDE disk is typically probed first by the BIOS, so
|
|
the first IDE disk is the first probed disk. The boot manager
|
|
you will install will be hooked into the MBR on this first
|
|
probed hard disk that we've just described.</para>
|
|
</sect2>
|
|
|
|
<sect2 id="limits">
|
|
<title>Booting Limitations and Warnings</title>
|
|
|
|
<para>Now the interesting stuff that you need to watch out
|
|
for.</para>
|
|
|
|
<sect3>
|
|
<title>The dreaded 1024 cylinder limit and how BIOS LBA helps</title>
|
|
|
|
<para>The first part of the booting process is all done
|
|
through the BIOS, (if that's a new term to you, the BIOS is
|
|
a software chip on your system motherboard which provides
|
|
startup code for your computer). As such, this first part
|
|
of the process is subject to the limitations of the BIOS
|
|
interface.</para>
|
|
|
|
<para>The BIOS interface used to read the hard disk during
|
|
this period (INT 13H, Subfunction 2) allocates 10 bits to
|
|
the Cylinder Number, 8 bits to the Head Number, and 6 bits
|
|
to the Sector Number. This restricts users of this
|
|
interface (i.e. boot managers hooked into your disk's MBR as
|
|
well as OS loaders hooked into the Boot Sectors) to the
|
|
following limits:</para>
|
|
|
|
<itemizedlist>
|
|
<listitem>
|
|
<para>1024 cylinders, max</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>256 heads, max</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>64 sectors/track, max (actually 63, <literal>0</literal>
|
|
isn't available)</para>
|
|
</listitem>
|
|
</itemizedlist>
|
|
|
|
<para>Now big hard disks have lots of cylinders but not a lot
|
|
of heads, so invariably with big hard disks the number of
|
|
cylinders is greater than 1024. Given this and the BIOS
|
|
interface as is, you can't boot off just anywhere on your
|
|
hard disk. The boot code (the boot manager and the OS
|
|
loader hooked into all bootable partitions' Boot Sectors)
|
|
has to reside below cylinder 1024. In fact, if your hard
|
|
disk is typical and has 16 heads, this equates to:</para>
|
|
|
|
<informalexample>
|
|
<para>1024 cyl/disk × 16 heads/disk × 63
|
|
sect/(cyl-head) × 512 bytes/sector</para>
|
|
</informalexample>
|
|
|
|
<para>which is around the often-mentioned 528MB limit.</para>
|
|
|
|
<para>This is where BIOS LBA (Logical Block Addressing) comes
|
|
in. BIOS LBA gives the user of the BIOS API calls access to
|
|
physical cylinders above 1024 though the BIOS interfaces by
|
|
redefining a cylinder. That is, it remaps your cylinders
|
|
and heads, making it appear through the BIOS as though the
|
|
disk has fewer cylinders and more heads than it actually
|
|
does. In other words, it takes advantage of the fact that
|
|
hard disks have relatively few heads and lots of cylinders
|
|
by shifting the balance between number of cylinders and
|
|
number of heads so that both numbers lie below the
|
|
above-mentioned limits (1024 cylinders, 256 heads).</para>
|
|
|
|
<para>With BIOS LBA, the hard disk size limitation is
|
|
virtually removed (well, pushed up to 8 Gigabytes anyway).
|
|
If you have an LBA BIOS, you can put FreeBSD or any OS
|
|
anywhere you want and not hit the 1024 cylinder
|
|
limit.</para>
|
|
|
|
<para>To use my 1.6 Gig Western Digital as an example again,
|
|
it's physical geometry is:</para>
|
|
|
|
<informalexample>
|
|
<para>(3148 cyl, 16 heads, 63 sectors/track, 512
|
|
bytes/sector)</para>
|
|
</informalexample>
|
|
|
|
<para>However, my BIOS LBA remaps this to:</para>
|
|
|
|
<informalexample>
|
|
<para>(787 cyl, 64 heads, 63 sectors/track, 512
|
|
bytes/sector)</para>
|
|
</informalexample>
|
|
|
|
<para>giving the same effective size disk, but with cylinder
|
|
and head counts within the BIOS API's range (Incidentally, I
|
|
have both Linux and FreeBSD existing on one of my hard disks
|
|
above the 1024th physical cylinder, and both operating
|
|
systems boot fine, thanks to BIOS LBA).</para>
|
|
</sect3>
|
|
|
|
<sect3>
|
|
<title>Boot Managers and Disk Allocation</title>
|
|
|
|
<para>Another gotcha to watch out when installing boot
|
|
managers is allocating space for your boot manager. It's
|
|
best to be aware of this issue up front to save yourself
|
|
from having to reinstall one or more of your OSs.</para>
|
|
|
|
<para>If you followed the discussion in <xref
|
|
linkend="booting"> about the Master Boot Sector (where the
|
|
MBR is), Partition Boot Sectors, and the booting process,
|
|
you may have been wondering just exactly where on your hard
|
|
disk that nifty boot manager is going to live. Well, some
|
|
boot managers are small enough to fit entirely within the
|
|
Master Boot Sector (Cylinder 0, Head 0, Sector 0) along with
|
|
the partition table. Others need a bit more room and
|
|
actually extend a few sectors past the Master Boot Sector in
|
|
the Cylinder 0 Head 0 track, since that's typically
|
|
free…typically.</para>
|
|
|
|
<para>That's the catch. Some operating systems (FreeBSD
|
|
included) let you start their partitions right after the
|
|
Master Boot Sector at Cylinder 0, Head 0, Sector 2 if you
|
|
want. In fact, if you give FreeBSD's sysinstall a disk with
|
|
an empty chunk up front or the whole disk empty, that's
|
|
where it'll start the FreeBSD partition by default (at least
|
|
it did when I fell into this trap). Then when you go to
|
|
install your boot manager, if it's one that occupies a few
|
|
extra sectors after the MBR, it'll overwrite the front of
|
|
the first partition's data. In the case of FreeBSD, this
|
|
overwrites the disk label, and renders your FreeBSD
|
|
partition unbootable.</para>
|
|
|
|
<para>The easy way to avoid this problem (and leave yourself
|
|
the flexibility to try different boot managers later) is
|
|
just to always leave the first full track on your disk
|
|
unallocated when you partition your disk. That is, leave
|
|
the space from Cylinder 0, Head 0, Sector 2 through Cylinder
|
|
0, Head 0, Sector 63 unallocated, and start your first
|
|
partition at Cylinder 0, Head 1, Sector 1. For what it's
|
|
worth, when you create a DOS partition at the front of your
|
|
disk, DOS leaves this space open by default (this is why
|
|
some boot managers assume it's free). So creating a DOS
|
|
partition up at the front of your disk avoids this problem
|
|
altogether. I like to do this myself, creating 1 Meg DOS
|
|
partition up front, because it also avoids my primary DOS
|
|
drive letters shifting later when I repartition.</para>
|
|
|
|
<para>For reference, the following boot managers use the
|
|
Master Boot Sector to store their code and data:</para>
|
|
|
|
<itemizedlist>
|
|
<listitem>
|
|
<para>OS-BS 1.35</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>Boot Easy</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>LILO</para>
|
|
</listitem>
|
|
</itemizedlist>
|
|
|
|
<para>These boot managers use a few additional sectors after
|
|
the Master Boot Sector:</para>
|
|
|
|
<itemizedlist>
|
|
<listitem>
|
|
<para>OS-BS 2.0 Beta 8 (sectors 2-5)</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>OS/2's boot manager</para>
|
|
</listitem>
|
|
</itemizedlist>
|
|
</sect3>
|
|
|
|
<sect3>
|
|
<title>What if your machine won't boot?</title>
|
|
|
|
<para>At some point when installing boot managers, you might
|
|
leave the MBR in a state such that your machine won't boot.
|
|
This is unlikely, but possible when re-FDISKing underneath
|
|
an already-installed boot manager.</para>
|
|
|
|
<para>If you have a bootable DOS partition on your disk, you
|
|
can boot off a DOS floppy, and run:</para>
|
|
|
|
<informalexample>
|
|
<screen>A:\> <userinput>FDISK /MBR</>
|
|
</screen>
|
|
</informalexample>
|
|
|
|
<para>to put the original, simple DOS boot code back into the
|
|
system. You can then boot DOS (and DOS only) off the hard
|
|
drive. Alternatively, just re-run your boot manager
|
|
installation program off a bootable floppy.</para>
|
|
</sect3>
|
|
</sect2>
|
|
</sect1>
|
|
</article>
|